In today's competitive automotive industry, it is becoming increasingly important for automotive manufacturers to deliver refined engines that offer strong performance while also balancing fuel economy considerations. Cylinder deactivation is being explored in the automotive industry as one option to increase fuel economy by deactivating certain cylinders of an engine when there is not a demand for such cylinders. Often such cylinder deactivation systems involve add on hardware that increases the cost and complexity of manufacturing the engines as well as requires additional parts that may increase the potential for long term durability concerns.
In addition, while the aforementioned cylinder deactivation systems are designed to improve fuel economy, such systems are generally not designed to increase engine performance. Similar to cylinder deactivation, the automotive industry has also been exploring variable lift valvetrains to improve engine performance under certain engine operating conditions. Generally, such variable lift systems have also required the addition of complex components that are independent of the cylinder deactivation hardware. These variable lift systems have thus resulted in a complex and costly valvetrain that is difficult to manufacture and potentially prone to durability issues.
Another disadvantage associated with both the cylinder deactivation systems and the variable lift systems is that the size and complexity of the add on hardware for each independent system results in a larger cylinder head that is difficult to package in today's relatively congested under hood engine compartment. Such a larger cylinder head is more expensive to manufacture and adds additional weight to the engine which is counterproductive to the goals of improving fuel economy and other engine performance characteristics.
Thus, there is a need for a compact valvetrain system having a rocker shaft arrangement that overcomes the aforementioned and other disadvantages.